Irrigation systems that deliver water, often containing plant nutrients, pesticides and/or medications, to plants via networks of irrigation pipes are very well known. In many such irrigation networks, water from an irrigation pipe is delivered to the plants by “emitters” or “drippers”, hereinafter generically referred to as emitters, which are connected to or installed along the length of the pipe. Each emitter comprises at least one inlet or an array of inlets through which water flowing in the pipe enters the emitter and an outlet through which water that enters the emitter exits the emitter. The emitter diverts a relatively small portion of water flowing in the pipe and discharges the diverted water to irrigate plants in a neighborhood of the location of the emitter.
Generally, to control rate of water discharge by the emitter, the emitter comprises a water flow and pressure reduction channel, a “labyrinth channel” or “labyrinth” through which water that enters the emitter must flow to reach the emitter outlet. The labyrinth channel is a high resistance flow channel along which pressure of water flowing through the emitter drops relatively rapidly with distance along the labyrinth channel from a relatively high water pressure which prevails substantially at or near the emitter inlet to a relatively low discharge pressure, generally a gauge pressure equal to about zero, substantially at or near the emitter outlet. The labyrinth channel generally comprises a tortuous “obstacle” flow path that generates turbulence in water flowing in the labyrinth to reduce water pressure and discharge of water by the emitter. Usually the obstacle path comprises a configuration of baffles that impede and introduce turbulence into water flow.
U.S. Pat. No. 4,060,200 to Mehouder, the disclosure of which is incorporated herein by reference, describes a labyrinth channel comprising two opposing arrays of equally spaced baffle “teeth” that extend out towards each other from opposite walls of the channel. Each tooth has a cross section perpendicular to the wall substantially in the shape of a truncated isosceles triangle, i.e. the apex of the triangle is “cut off”. The arrays of baffle teeth are substantially mirror images of each other but are displaced relative to each other along the channel by half a repeat period of the baffle teeth, i.e. by half the distance between adjacent baffle teeth. A tooth in one baffle array therefore faces a point in a space, hereinafter a “bay” substantially half way between adjacent baffle teeth in the other array. The tips of two adjacent baffle teeth in one baffle array in the labyrinth and the tip of the tooth in the opposing baffle array that faces the bay formed by the adjacent baffle teeth are substantially coplanar.
U.S. Pat. No. 5,207,386, the disclosure of which is incorporated herein by reference, also to Mehoudar, describes a labyrinth channel comprising a central “through-flow” flow channel that does not comprise impediments to water flow. The impediment free through-flow channel is flanked on either side by an array of equally spaced, symmetric baffle teeth, similar to the arrays of baffle teeth described in U.S. Pat. No. 4,060,200. As in U.S. Pat. No. 4,060,200, the baffle teeth arrays in U.S. Pat. No. 5,207,386 are displaced relative to each other along the labyrinth channel by half a repeat period of the baffle teeth.
U.S. Pat. No. 5,207,386 notes that a labyrinth channel comprising a central, impediment free through-flow channel, provides greater reduction in water flow pressure per unit length of the labyrinth than other labyrinth channels. The patent provides a range for the width of the through-flow channel and an optimum for its width relative to dimensions of the baffle teeth. The patent notes that the increased pressure reduction functionality results in a “comparatively low” sensitivity of outflow of water from an emitter to changes in inlet water pressure to the emitter. In addition, the improved pressure reduction functionality enables shorter labyrinth channels to be used to reduce water pressure in emitters, and as a result enables emitters to be produced less expensively.
US Patent Publication 2003/0150940, the disclosure of which is incorporated herein by reference, shows a labyrinth channel comprising two opposing rows of equally spaced baffle “fingers” that extend out towards each other from opposite walls of the channel. The tips of the finger baffles are terraced so that tips of the fingers decrease step-wise in size with height of the fingers off the floor of the channel. The labyrinth channel does not comprise a through-flow channel and tips of fingers in each row extend into spaces between fingers of the other row, i.e. the fingers mesh. All the fingers appear to be tilted at a same angle towards a downstream direction of water flow.
PCT publication WO 00/01219, the disclosure of which is incorporated herein by reference, describes a “sawblade-shaped zig-zagging” pattern comprised in a fluid flow regulatory channel of an irrigation pipe. The zig-zagging pattern is embossed on a relatively thin web of flexible plastic material. The web is folded over so that longitudinal edges of the web overlap and regions of the overlapping edges are welded to form the irrigation pipe and regulatory channel comprising the zig-zagging pattern.